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 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.security;

import java.util.*;

/**
 * Abstract class representing a collection of Permission objects.
 *
 * <p>With a PermissionCollection, you can:
 * <UL>
 * <LI> add a permission to the collection using the {@code add} method.
 * <LI> check to see if a particular permission is implied in the
 * collection, using the {@code implies} method.
 * <LI> enumerate all the permissions, using the {@code elements} method.
 * </UL>
 *
 * <p>When it is desirable to group together a number of Permission objects
 * of the same type, the {@code newPermissionCollection} method on that
 * particular type of Permission object should first be called. The default
 * behavior (from the Permission class) is to simply return null.
 * Subclasses of class Permission override the method if they need to store
 * their permissions in a particular PermissionCollection object in order
 * to provide the correct semantics when the
 * {@code PermissionCollection.implies} method is called.
 * If a non-null value is returned, that PermissionCollection must be used.
 * If null is returned, then the caller of {@code newPermissionCollection}
 * is free to store permissions of the
 * given type in any PermissionCollection they choose
 * (one that uses a Hashtable, one that uses a Vector, etc).
 *
 * <p>The PermissionCollection returned by the
 * {@code Permission.newPermissionCollection}
 * method is a homogeneous collection, which stores only Permission objects
 * for a given Permission type.  A PermissionCollection may also be
 * heterogeneous.  For example, Permissions is a PermissionCollection
 * subclass that represents a collection of PermissionCollections.
 * That is, its members are each a homogeneous PermissionCollection.
 * For example, a Permissions object might have a FilePermissionCollection
 * for all the FilePermission objects, a SocketPermissionCollection for all the
 * SocketPermission objects, and so on. Its {@code add} method adds a
 * permission to the appropriate collection.
 *
 * <p>Whenever a permission is added to a heterogeneous PermissionCollection
 * such as Permissions, and the PermissionCollection doesn't yet contain a
 * PermissionCollection of the specified permission's type, the
 * PermissionCollection should call
 * the {@code newPermissionCollection} method on the permission's class
 * to see if it requires a special PermissionCollection. If
 * {@code newPermissionCollection}
 * returns null, the PermissionCollection
 * is free to store the permission in any type of PermissionCollection it
 * desires (one using a Hashtable, one using a Vector, etc.). For example,
 * the Permissions object uses a default PermissionCollection implementation
 * that stores the permission objects in a Hashtable.
 *
 * <p> Subclass implementations of PermissionCollection should assume
 * that they may be called simultaneously from multiple threads,
 * and therefore should be synchronized properly.  Furthermore,
 * Enumerations returned via the {@code elements} method are
 * not <em>fail-fast</em>.  Modifications to a collection should not be
 * performed while enumerating over that collection.
 *
 * @author Roland Schemers
 * @see Permission
 * @see Permissions
 */

public abstract class PermissionCollection implements java.io.Serializable {

  private static final long serialVersionUID = -6727011328946861783L;

  // when set, add will throw an exception.
  private volatile boolean readOnly;

  /**
   * Adds a permission object to the current collection of permission objects.
   *
   * @param permission the Permission object to add.
   * @throws SecurityException -  if this PermissionCollection object has been marked readonly
   * @throws IllegalArgumentException - if this PermissionCollection object is a homogeneous
   * collection and the permission is not of the correct type.
   */
  public abstract void add(Permission permission);

  /**
   * Checks to see if the specified permission is implied by
   * the collection of Permission objects held in this PermissionCollection.
   *
   * @param permission the Permission object to compare.
   * @return true if "permission" is implied by the  permissions in the collection, false if not.
   */
  public abstract boolean implies(Permission permission);

  /**
   * Returns an enumeration of all the Permission objects in the collection.
   *
   * @return an enumeration of all the Permissions.
   */
  public abstract Enumeration<Permission> elements();

  /**
   * Marks this PermissionCollection object as "readonly". After
   * a PermissionCollection object
   * is marked as readonly, no new Permission objects can be added to it
   * using {@code add}.
   */
  public void setReadOnly() {
    readOnly = true;
  }

  /**
   * Returns true if this PermissionCollection object is marked as readonly.
   * If it is readonly, no new Permission objects can be added to it
   * using {@code add}.
   *
   * <p>By default, the object is <i>not</i> readonly. It can be set to
   * readonly by a call to {@code setReadOnly}.
   *
   * @return true if this PermissionCollection object is marked as readonly, false otherwise.
   */
  public boolean isReadOnly() {
    return readOnly;
  }

  /**
   * Returns a string describing this PermissionCollection object,
   * providing information about all the permissions it contains.
   * The format is:
   * <pre>
   * super.toString() (
   *   // enumerate all the Permission
   *   // objects and call toString() on them,
   *   // one per line..
   * )</pre>
   *
   * {@code super.toString} is a call to the {@code toString}
   * method of this
   * object's superclass, which is Object. The result is
   * this PermissionCollection's type name followed by this object's
   * hashcode, thus enabling clients to differentiate different
   * PermissionCollections object, even if they contain the same permissions.
   *
   * @return information about this PermissionCollection object, as described above.
   */
  public String toString() {
    Enumeration<Permission> enum_ = elements();
    StringBuilder sb = new StringBuilder();
    sb.append(super.toString() + " (\n");
    while (enum_.hasMoreElements()) {
      try {
        sb.append(" ");
        sb.append(enum_.nextElement().toString());
        sb.append("\n");
      } catch (NoSuchElementException e) {
        // ignore
      }
    }
    sb.append(")\n");
    return sb.toString();
  }
}
